1. Field of the Invention
The present invention relates to a foreign matter removal method and a storage medium, and in particular to a foreign matter removal method that removes foreign matter attached to a surface of a semiconductor substrate after plasma etching processing.
2. Description of the Related Art
If a plasma processing, for example, a plasma etching processing is carried out on a wafer as a substrate using plasma produced from a CF-type process gas, CF-type deposit arising from the CF-type process gas may become attached to a surface of the wafer. The CF-type deposit attached to the surface of the wafer is removed by sputtering using plasma (positive ions), but the CF-type deposit attached to a peripheral edge (hereinafter referred to as the “bevel portion”) of the wafer cannot be removed because the bevel portion resists sputtering by plasma.
To cope with this, the CF-type deposit (for example, BSP) attached to the bevel portion is removed using a postprocessing apparatus. Specifically, the postprocessing apparatus heats the bevel portion of the wafer by irradiation with laser light, and supplies ozone gas toward the bevel portion so that the CF-type deposit can be decomposed into CO, CO2, and F2 through a chemical reaction and removed.
In the postprocessing apparatus that removes foreign matter attached to the surface of the wafer using laser light, before the wafer is transferred from a processing chamber (reaction chamber) into a postprocessing chamber and mounted on a mounting stage (stage) in the postprocessing chamber, it is necessary to detect and correct for a misalignment of the wafer.
As a method of correcting for a misalignment of the wafer or aligning the wafer in such a substrate processing apparatus, a method has conventionally been adopted in which the wafer is centered on the stage of the substrate processing apparatus while the amount of misalignment is monitored using a CCD camera and the misalignment is corrected for, or a method in which a jig (hereinafter referred to as the “stage plate”) is mounted on the stage, and the wafer is mounted on the stage plate.
However, the method using the CCD camera has the disadvantage that the apparatus is expensive, there is a need to provide space for the CCD camera, and the CCD camera must be calibrated on a regular basis. Also, the method using the stage plate has the problem that the amount of misalignment becomes large because the amounts of misalignment are integrated due to a large number of times of alignment.
FIGS. 7A and 7B are views useful in explaining the problem of the substrate alignment method using the stage plate, in which FIG. 7A is a plan view of a wafer W mounted on the mounting stage in the substrate processing apparatus, and FIG. 7B is a side view of FIG. 7A.
Referring to FIGS. 7A and 7B, a stage 71 as the mounting stage is connected to a motor 73 via a shaft 72, and at the stage of alignment of the shaft 72 with respect to the stage 71, a misalignment 7A arises between the center of the shaft 72 and the center of the stage 71. Also, when a stage plate 74 is mounted on the stage 71, a misalignment 7B arises between the center of the stage 71 and the center of the stage plate 74. Further, when the wafer W is positioned on the stage plate 74, a misalignment 7C arises between the center of the stage plate 74 and the center of the wafer W. Thus, the final misalignment of 7A+7B+7C arises between the center of the shaft 72 and the center of the wafer W. Also, when various kinds of processing are carried out on the wafer W, the width of misalignment may gradually increase.
If the wafer W with the center position thereof misaligned is transferred to the postprocessing apparatus and mounted on the stage as the mounting stage by a transfer robot, postprocessing will automatically be performed on the wafer W remaining misaligned. Thus, a technique for detecting and correcting for the misalignment of the wafer W mounted on the stage in the postprocessing apparatus so as to properly carry out postprocessing has been demanded.
On the other hand, examples of publications disclosing prior arts in which a wafer W as a substrate to be processed is aligned by detecting the position of a notch in the wafer W include Japanese Laid-Open Patent Publication (Kokai) No. H05-206250. Japanese Laid-Open Patent Publication (Kokai) No. H05-206250 discloses the technique that laser light is irradiated on an outer end face of the wafer W on the stage from a horizontal direction, a reflected wave is received by a laser light-receiving unit to form an image, the position of a notch is recognized based on an image forming position varying according to whether the outer end face is far or near, and a misalignment of the wafer W is detected and corrected for based on the position of the notch and an output from a rotation angle detection unit.
However, the above prior art has the problem that a laser light irradiation unit and a light-receiving unit for exclusive use in aligning a substrate are needed, and hence the apparatus has to be large in size, resulting in elevated costs of the apparatus.